package java111_2;

import java.util.Arrays;
import java.util.Scanner;

public class Day43 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int n = in.nextInt();
            int m = in.nextInt();
            double res = 1;
            double res1 = 1;
            double res2 = 1;
            for (int i = 0; i < m; i++) {

                res1 *= (n - i);
                res2 *= (i + 1);
            }
            res = res1 / res2 * Math.pow(0.8, m) * Math.pow(0.2, n-m);
            System.out.printf("%.4f", res);
            System.out.println();
        }
    }


    public static void main2(String[] args) {
        // 暴力解法超时O(N^2) 排序 + 二分 通过O(N * logN)
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int n = in.nextInt();
            long l = in.nextInt(), r = in.nextInt(), res = 0;
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = in.nextInt();
            }
            Arrays.sort(arr);
            for (int i = 0; i < n-1; i++) {
                int start, end;
                int left = i, right = n - 1;
                while (left < right) {
                    int mid = left + (right - left + 1) / 2;
                    if (arr[mid] - arr[i] < l) {
                        left = mid;
                    } else {
                        right = mid - 1;
                    }
                }
                start = left;
                left = i;
                right = n - 1;
                while (left < right) {
                    int mid = left + (right - left) / 2;
                    if (arr[mid] - arr[i] > r) {
                        right = mid;
                    } else {
                        left = mid + 1;
                        if(left == n-1 && arr[left] - arr[i] <= r && arr[left] - arr[i] >= l){
                            res += 1;
                        }
                    }
                }
                end = left;
                if(end > start) {
                    res += end - start - 1;
                }
            }
            System.out.println(res);
        }
    }
}
